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 RCU Review: Bohemia Models Monocoupe More On This Product
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Monocoupe
Bohemia Models
Electric Conversion
by
Greg Covey
[email protected]
INTRODUCTION
CONSTRUCTION
FLIGHT REPORT
MODEL SPECIFICATIONS Wingspan:
Length:
Wing Area:
Weight:
Airfoil:
Wing Loading:
Retail Price:
Manufacturer:
Distributor: 82" (2080 mm)
50" (1380 mm)
1054 sq. in. (68 dm2)
160 oz. (4536g)
Unknown
21.9 oz. sq/ft.
$379.00
Bohemia Models
Hobby Lobby
SUMMARY
PRODUCT INFORMATION
USED IN THIS REVIEW Motor:
Receiver:
No. of
Channels:
Servos:
Radio:
Battery:
ESC: AXI 4120/14 Rotating can motor.
Hitec Supreme 7-Ch. Receiver
5 (ailerons, flaps, rudder, elevator,
.throttle)
Hitec HS-85BB Servos (ailerons-2,
Elevator, Rudder)
Futaba Super-8
14-Cell HR-SC2600mAh NiMH
Jeti Advance 70-3P Opto
I N T R O D U C T I O N HISTORY OF 1928 "Monocoupe"
The Monocoupe 22, the prototype of the 70, was the first light cabin monoplane to be certificated under
the Department of Commerce regulations established in 1927. In 1928, nearly 90 percent of all the light
airplanes produced and sold in the United States were Monocoupes. The popularity of this light cabin
plane lay in the side-by-side seating and the pleasant, though spirited, characteristics of the aircraft that
made it fun to fly.
In the mid-1920s a young advertising man named Don Luscombe flew his open cockpit JN-4D "Jenny"
in and out of a small airstrip in Davenport, Iowa, he thought about how much nicer it would be if he
could fly in a relatively small enclosed-cabin airplane. Then he could dress in a business suit rather
than the usual helmet, goggles, and flight coveralls of the day, and arrive at his destination ready for
business or pleasure. He decided to build his own aircraft, a two-place, side-by-side cabin monoplane
with a simple but strong structure and a powerful engine. Luscombe was somewhat influenced by the
design of the rather rakish-looking Belgian Delmonty-Poncelet Limousine, a high-wing monoplane with
a side-by-side enclosed cabin and the reverse curve rear fuselage lines that were to become one of
the signature identifier features of the Monocoupes. Luscombe's mock-ups impressed his companions
in the Davenport Flying Club so well that, in October 1926, they raised $5,000 to help him start the
Central States Aero Company. To build his dream, Luscombe hired a young self-taught designer by
the name of Clayton Folkerts who was to later design championship racing airplanes of the 1930s.
Folkerts built the first prototype, Mono #1, almost single handedly, in about 4 ½ months and E.K.
"Rusty" Campbell made the first test flight on April 6, 1927. The airplane configuration was a two-place,
side by side, strut-braced high wing monoplane with a conventional tailskid and main wheel landing
gear. The fuselage and tail structure was of welded steel tubing. The one-piece wing was constructed
with routed solid spruce spars and the ribs were constructed of spruce and basswood. The entire
airplane was covered with Grade A cotton.
Mono #1 received a lot of interest, but just as Luscombe began to think about customers, a
fundamental change in aircraft production occurred. The U.S. Department of Commerce Aeronautics
branch instituted the Approved Type Certificate (ATC) program requiring all potential commercial
aircraft designs to undergo analysis and test for a type certificate. Because Folkerts did not have
formal training in engineering, Central States hired university graduate Jerome Lederer, a consulting
aeronautical engineer, to verify the performance predictions and the structural integrity of the airplane.
Lederer hired two graduate aeronautical engineers, Fred Knack and Bud Whelan, to help in the
certification process. Luscombe's and Folkerts' basic design proved to be sound and ATC #22 was
awarded to the Monocoupe in January 1928.
The name Monocoupe referred to the marriage of a monoplane and the coupe, the two-passenger
enclosed car. The first model was known as the Monocoupe Model 22 (after its ATC number) and a
total of 20 Mono 22s were built. The engine, a Detroit Air Cat air-cooled radial proved to be problematic
and several others, including the expensive Anzani, were tried. The solution appeared in the form of
the Velie M-5 five-cylinder radial, a similar but more reliable engine than the Air Cat. The engine was
nominally rated at 55 hp with maximum of 62 hp available for take-off. The Velie engine came from the
highly successful Velie Motors Corporation in Moline, Illinois, and the compatibility of this engine and
aircraft encouraged the Velie family to support Luscombe and go into full-time aircraft production.
Central States Aero moved just across the Mississippi River to Moline and became Mono-Aircraft Inc.,
a subsidiary of Velie Motors.
The installation of the Velie engine into the Monocoupe airplane, along with a few minor improvements,
resulted in the Monocoupe 70 that was issued its Approved Type Certificate (ATC 70) in September
1928. In June 1928, Phoebie Omlie, a racing pilot, announced her intent to fly her Velie-powered
Monocoupe Chiggers in the National Air Tour and with it she also won the lightweight division of the
Women's Air Derby in August 1928. The Monocoupe 70 flew at air races around the country with
Omlie, Johnny Livingston, and Vern Roberts. Luscombe established dealers and distributors around
the country and even wrote a book entitled Simplified Flying for advertising purposes. More than 350 of
the Model 70 and its incrementally improved companion Model 113 (ATC 113 issued Feb. 1929) were
produced. The flashy good looks did not come cheaply though, as it cost between $2,500 and $3,000
to buy. While the standard Models 70, 110, 113 and 125 were more docile to fly than the 110 and 113
Specials, it really was not an airplane for the novice pilot.
George Law purchased Monocoupe Model 70, NC6730, serial number 133, in July 1928 and it went
through a succession of sixteen owners before it was severely damaged in a crash in 1940. Robert
and Glen Jordan sold the aircraft when it was declared not airworthy and three additional owners
passed it along until it was given to famous racing and test pilot Tony LeVier in 1975. He acquired title
in March 1978 and had the aircraft restored with its striking black fuselage and vertical tail with orange
wings and horizontal tail. Some people suggest that the only original parts of the airplane are the
nameplate and the paperwork, nonetheless, it is one of only a few of the famous type still in existence.
LeVier donated it to NASM on December 12, 1983, and it was stored in California until it was lent to
the California Museum of Science and Industry in Los Angeles in 1984.
Copyright © 1998-2000 National Air and Space Museum, Smithsonian Institution
Full Scale Specs
Wingspan
9.7 m (32 ft)
Length
6 m (19 ft 9 in)
Height
1.9 m (6 ft 3 in)
Weight
Empty 360 kg (795
lb)
INTRODUCTION
When I first saw the Bohemia Model's Monocoupe, I couldn't help but think of the history behind the
plane. The short "snub" nose wasn't pretty, but, it was needed to balance the plane with the heavy
rotary engine.
I also had the opportunity to test a new larger size outrunner motor from AXI. It installed easily behind
the firewall and could spin a 13" prop without the need for a gearbox.
The quality of the ARF construction, and, overall size of the plane with its 81.5" wingspan, provided for
an enjoyable conversion to electric power! All the parts were carefully wrapped in either foam or
bubble-wrap. Only my wing halves needed a touch-up with the heat gun on a few small areas.
Kit Contents after they are unwrapped C O N S T R U C T I O N TAIL ASSEMBLY
I started my tail assembly by first mounting the servos in the fuselage. I built the elevator and rudder
servo assembly outside the plane and then installed it into position before gluing with 5-minute epoxy.
The servos were first mounted on
the posts outside The entire assembly was then glued
into place I placed the horizontal stabilizer on the fuselage tail and traced an outline onto the stabilizer with a
black marker pen. This included the leading edge notch that will align with the vertical stabilizer leading
edge post and also with the slot in the fuselage tail.
The elevator halves are joined together by gluing the pre-bent joiner rod into the pre-drilled holes and
channel slots. I used 5-minute epoxy. Before attaching the elevator and rudder to the stabilizers, I cut
the ends off of each side of the supplied nylon hinges. I cut through the outer set of holes to shorten the
length of the hinge. This allowed it to fit into the slots easier. I then glued the hinges onto the stabilizers
using a small amount of 5-minute epoxy. Finally, the control surfaces (elevator and rudder) were attached.
The clevis was CA'ed onto the
tail ends of each control rod Both stabilizers were glued at the
same time using 5-minute epoxy Once test fitted, both stabilizers were glued onto the fuselage tail at the same time using 5-minute
epoxy. I then mounted the control horns per the diagram and attached the clevis to insure good
alignment. Be sure that the 4 adjustment holes on the control horn are in-line with the gap between
the stabilizer and the control surface. Since the control surfaces are rather large, it is important for
the servo to have the best mechanical advantage (or leverage) to move them. Having the control
horn swivel directly over the hinge line also provides for equal throw in either direction.
The control horn holes are mounted
over the hinge for best leverage The fixed position tailwheel mounts
easily with supplied hardware
The fixed position tail wheel mounted easily with 2 screws and a custom plywood cover. The
undercarriage and wheels also installed easily with the supplied plastic fixtures, screws, and
self-locking nuts. I choose not to install the balsa planks on the undercarriage to reduce drag in-flight.
The undercarriage and painted
wheels also installed easily All the plastics were cut and sanded smooth before
test fitting into position At this point, I cut all the plastics using scissors and sanded the edges smooth with a fine grit
sandpaper. I later choose not to use the wing servo covers.
WING ASSEMBLY I skipped over the black laminate cover for now and did a test fit of the wings after first installing the
two metal rods in the center section. When I was satisfied with the fit, I decided at this point that I
would not be using the flaps. I felt that the plane would take-off, fly, and land relatively slow without
flaps due to the aggressive airfoil design and rather large wing area. I taped the flaps up using clear
cellophane tape.
The wings were test fitted and measured to
be 81.5" long Plenty of table space is needed to
assemble a model this size The servo bays were very nicely set up to accommodate various sizes. My Hitec HS-85BB "Mighty
Micro" ball bearing servos are smaller than standard size servos but they fit perfectly without
modification. I mounted the servo onto the supplied posts first and then routed the extended servo lead
through the wing with the help of a spare metal control rod.
The white control lever was epoxied into the aileron and the two black suspension levers were glued
into the wing at the same time. Be sure to align these levers in the proper direction. While the epoxy
was drying, I soldered the brass caps onto the control rods. The remainder of the linkage was
assembled per the manual diagram on page 9. You may need to cut the metal control rod length
before soldering.
My Hitec HS-85BB "Mighty Micro"
servos fit without modification The "Y" adapter input lead was
extended to reach the receiver To finish the wing assembly, I installed the eye hooks into the fuselage end of each wing half after first
opening them up half way. This allowed them to extend inside the wing center section and provided an
easier connection for the rubber band support. A longer eye hook would have worked better here.
The wing halves were then fitted onto the center section. To test the ailerons, I connected the servo
leads to a "Y" adapter in the center section that extended down into the fuselage to the receiver. The
single input of the "Y" adapter was lengthened with a 12" piece of ribbon cable. Alternatively, you could
also purchase another 12" extension cable.
The eyelet hooks were opened up to
provide easier access The wooden dowels and Velcro
allowed for easy wing assembly My ailerons tested out fine and needed only a minor adjustment for proper alignment. The black
plastic wing center cover was mounted using several small wooden dowels in the front and Velcro on
the back. This provided easy access for wing assembly in the field
POWER SYSTEM:
Since I was using an AXI 4120/14 outrunner motor, I decided to try to balance the plane with the motor
mounted behind the firewall. This made it easy to mount the motor with four M4 screws, and, as it
turned out, the plane balanced fine using my 14-cells of HR-SC2600mAh NiMH. When mounting the
motor directly against the firewall, I needed to slightly counter-bore a larger diameter hole in the rear of
the firewall. This allowed room for the motor shaft holding clip to rotate. Alternatively, you could add
some thin washers on the M4 screws in-between the motor and the firewall.
I decided to install my battery packs, one 8-cell pack and one 6-cell pack, from the front of the model
just below the firewall. I routed the connection from the combined packs to the ESC outside the bottom
of the fuselage. This would allow me to screw on the front cover and easily re-charge the packs in the
field without removing them.
AXI 4120/16 Power setup Since I was using an Opto-coupled Jeti ESC, it had no Battery Eliminator Circuit (BEC). Instead of using
a separate receiver battery, I used an Ultimate BEC (or UBEC) from Kool Flight Systems. The
Ultimate BEC is an external circuit that taps power from your battery pack and regulates the voltage to
the necessary 5 volts to power your receiver and servos. It does not replace the speed control.
However, it provides the BEC function in a speed control with much more capabilities.
Power Setup
AXI 4120/14
Power Supply
Current
Prop
Gear Ratio
RPM
Battery
Battery Type
SETUP
14-cells
43 Amps
APC 13x8 e-prop
none
8200
HR-SC2600mAh
NiMH
FINAL ASSEMBLY:
The kit provides an addendum sheet to the manual along with the pins to allow easier assembly and
disassembly of the wing support struts in the field. The support struts are stored with the wing halves
and connected to the fuselage using the new pins. The strut modification allows for
easy wing assembly in the field For a better scale appearance, I created some mock cylinder heads from wine bottle corks. By cutting
the cork both lengthwise and widthwise, I created 4 heads. A second cork was needed for the 5th
head to simulate the original Velie M-5 five-cylinder radial engine look. I painted the heads silver and
CA'ed them to the painted firewall. A blackHLHS200
2"
spinner completed the look. The cylinder heads were made from cork
The finished Monocoupe looks very
scale.
READY TO FLY
The kit comes with decals already applied to complete the authentic look of the aircraft. I tested my
power system with the 14-cell, 2600mAh NiMH pack and APC 13x8 e-prop. I measured 8200 RPMs at
43amps. The pull felt very strong and made me confident that it would be sufficient power for this
plane. I was Ready-To-Fly (RTF) at about 160oz (or 10lbs).
F L I G H T R E P O R T TAKEOFF:
The model had plenty of power for a grass takeoff into a 10mph breeze. The huge wing area lifted
the plane easily and gently. The tailwheel lifted first and then the whole plane. The Monocoupe
took-off with authority into clear, blue sky!
FLIGHT PERFORMANCE:
I expected the model to fly well but I was surprised at just how much power the AXI rotating can
motor provided. I could easily cruise around at 1/2 throttle in a 10mph breeze. The plane wanted to
continue climbing so I added a few clicks of down trim to the elevator to obtain level flight.
Our maiden flight was with a 10 mph breeze that shifted directions. Although it handled well, this is
probably the most wind that I would fly the model in. You will get a more relaxed flight with 0-5mph
winds.
There were no bad stall characteristics exhibited and the model turned very well with just the rudder
control. Aileron turning was fun, and, as expected, I didn't miss having flaps. My smoothest turns were
made with a combination of rudder and ailerons. My Futaba Super-8 transmitter can easily program
the needed mix of rudder and aileron but I used both sticks for turning on the initial flights. We had fun
taking turns on the sticks and talking about increasing the scale looks even further.
LANDING:
Landings were simple but can be fast if you don't properly reduce speed. The model has plenty of lift
so it can require a large area to land comfortably. Although flaps would help in slowing the plane
down for landings, I feel that using a proper approach is best for this design, although, this is likely
just my personal preference. We had plenty of power for a few "touch-n-gos" before landing.
The plane is large and easy to see in the air. When landing, the front wheels touch down first and
then the tail wheel.
CONCLUSION:
The Monocoupe turned out to be an easy electric conversion project. Using the direct drive AXI
rotating can brushless motor eliminated the need for a gearbox and made for a simple installation
behind the firewall. The power system proved to be an excellent choice for this rather large historic
model. There are no brushes or gears to wear out. The ease of maintenance on a direct drive
solution is very attractive. Since it will fly in some wind, and, take-off from grass with authority, I plan
to fly my Monocoupe often in the upcoming Summer months.
S U M M A R Y 1-POOR 2-NEEDS IMPROVEMENT 3-AVERAGE 4-VERY GOOD 5-EXCELLENT
Packaging: Take-Off: Landing: Basic Aerobatics Low Speed Flight:
Construction: Hardware: High Speed Flight:
Instruction Manual: Ease of Assembly: Stall Characteristics: Kit Completeness: Scale Flight:
Finish Quality: HITS MISSES Wing Eye Hooks too short Very Scale looking High quality, solid construction Short assembly time Excellent scale performance Good Parts Fit Easy conversion to electric Easy field wing assembly The 1928 Monocoupe from Bohemia Models is a great electric
conversion. Check out Hobby Lobby for more information on this
great model. 1928 Monocoupe E-Conversion May 2003 P R O D U C T I N F O R M A T I O N Hobby Lobby International
5614 Franklin Pike Circle
Brentwood, N.J. 37027 USA
Tel: 615-373-1444
Email: [email protected]
Web Site: www.hobby-lobby.com
Hitec RCD USA, Inc.
12115 Paine St.
Poway CA, 92064
Phone: 858.748.6948
Fax: 858.748.1767
Web Site: www.hitec.com
Kool Flight Systems
Ultimate BEC (UBEC)
Available at Hobby Lobby Int.
Comments on RCU Review: Bohemia Models Monocoupe
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The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply
generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in
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